Browsing by Author "Cordeiro, Pedro"

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    Further evidence of Rhyacian arc magmatism in the basement of the Brasilia Belt, western Sao Francisco pericraton
    (2020) Filgueiras, Bernardo de Carvalho; de Oliveira, Claudinei Gouveia; Cordeiro de Sousa, Isabela Moreno; Cordeiro, Pedro
    A recently mapped area in central Brazil revealed a slice of Paleoproterozoic basement within Neoproterozoic metasedimentary rocks of the Brasilia Belt. The area, named here the Artulandia area for its proximity to the homonymous village, contains metatonalites and metagranodiorites in tectonic contact with a meta-volcanosedimentary sequence that encompasses felsic, intermediate and mafic metavolcanic rocks interlayered with clastic and chemical metasedimentary rocks. A sample of felsic orthogneiss from the metavolcano-sedimentary sequence, yielded a U-Pb zircon age of 2142 +/- 4.4 Ma, which is interpreted as the crystallization age of the volcanic protolith. Samples from the metagranite unit returned U-Pb zircon ages of 2130 +/- 7.4 Ma for a biotite metatonalite, 2157 +/- 9 for a biotite metagranite, and 2147 +/- 5 Ma for a sulfide-bearing meta-granodiorite, indicating roughly contemporaneous plutonic activity. Whole-rock geochemistry shows calcalkaline signatures for both units, and trace element results are compatible with an extensional setting, such as back-arc or intra-arc, for the metavolcano-sedimentary sequence, and a magmatic arc system for the metagranite unit. These rocks were generated in an episode of juvenile crust formation, as suggested by epsilon(Nd)(2.14Ga) values between 0 and +3.18. Based on lithological association, age and chemical signature, we suggest that the studied rocks represent a lateral continuation of the Campinorte Arc beyond the Rio Maranhao Thrust. Thus, the occurrence of Campinorte Arc rocks on both sides of the thrust argues against the thrust being a Neoproterozoic collisional suture. The geology of the Artulandia area in the context of the Campinorte Arc attests to the complexity of the Rhyacian amalgamation that generated the Sao Francisco Paleocontinent during a Rhyacian Orogeny.
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    Metamorphic disturbances of magnetite chemistry and the Sm-Nd isotopic system of reworked Archean iron formations from NE Brazil
    (2022) Moraes, Joice Dias de; Cordeiro, Pedro; Abrahao Filho, Eduardo; Oliveira, Juliana Rezende; Filho, Carlos Victor Rios da Silva
    Iron formations are valuable archives of sedimentary conditions and post-depositional events. However, geochemical proxies commonly used to determine genetic characteristics can be variably modified during metamorphism and deformation, hampering their use as records of regional geological events. This work focuses on strongly reworked magnetite-quartz-rich rocks from the Sao Jose do Campestre Massif, one of the oldest fragments of preserved crust in South America. The genetic classification of these magnetite-quartz-rich rocks is not straightforward because primary assemblages and textures were variably modified by granulite facies metamorphism during a regional Paleoproterozoic migmatization event. To address genetic ambiguities, we analyzed their magnetite and pyroxene chemistry, wholerock geochemistry, and Sm-Nd isotopes. Magnetite chemistry indicates that pyroxene-poor iron formations (Type B) are low in trace elements such as Ti, Al, V, and Mn, suggesting a chemical similarity to iron formations elsewhere. In contrast, magnetites from pyroxene-enriched Type A iron formations are rich in trace elements and more akin to magnetite crystallized from higher temperature systems, such as skarn and IOCG. The 147Sm/144Nd of these rocks show substantial variation even at the outcrop scale, indicating a locally-controlled, highly heterogeneous mixture of Archean, Paleoproterozoic, and Neoproterozoic sources. Therefore, our geochemical tools point out to heterogenous signatures of these magnetitequartz rocks and proxies compatible with both low and high-temperature conditions and age of deposition spanning sources from the Archean to the Neoproterozoic. We interpret that the studied Sao Jose do Campestre magnetite-quartz rocks represent Archean iron formations with original magnetite chemistry and isotopic signatures variably modified by metamorphism and by at least one deformation-related hydrothermal event. These results contrast with similar examples from China and Greenland where iron formations either preserved the magnetite chemistry or the primary isotopic signatures. Our study indicates that metamorphism can selectively affect chemical proxies used to study iron formations and undermine the genetic classification of iron ores. Thus, these proxies should be carefully applied in the interpretation of syn-depositional environments of polydeformed belts.(c) 2020 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
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    Microanalytical investigation of K-rich fenites from the Catalao II alkaline-carbonatite complex in Central Brazil: Implications for ore-forming processes within the world's largest niobium province
    (2024) Velasquez-Ruiz, Felipe; Reich, Martin; Cordeiro, Pedro; Lagoeiro, Leonardo; Angerer, Thomas
    Alkaline-carbonatite complexes are the main source of critical raw materials such as niobium (Nb) and rare earth elements (REE), which concentrate through a combination of magmatic and carbohydrothermal processes. These systems typically occur in close spatial connection with altered country rocks resulting from metasomatic alteration by exsolved K-Na-rich fluids, a process known as fenitization. Thus, the association between Nb-REE-rich carbonatites and fenites provides a unique opportunity for the investigation of carbohydrothermal alteration processes leading to critical metal enrichment. In this study, we focused on K-rich fenites associated with a shallow dike swarm system in the Boa Vista niobium deposit, the second-largest global producer of Nb, which is hosted within the Catal & atilde;o II alkaline-carbonatite complex in Central Brazil. We used a combination of micro-analytical techniques including EBSD, EMPA, and mu-EDXRF to unravel the complex micro-textural features of the fenites. Our data suggest that alkaline fluids exsolved vigorously from the carbonatite melts upon dike emplacement and pervasively metasomatized the country rocks, forming a melanocratic proximal fenite (phlogopitite), and distal fine-grained orthoclase-phlogopite-calcite fenites. Fluid alteration mobilized soluble cations (K, Fe, Mg, Ba, and Sr) plus S, CO2 and OH-, whereas Nb and REE were retained in the carbonatite dikes. The consistent dike-orthogonal orientation of metasomatic phlogopite and orthoclase grains in the proximal fenite, determined by EBSD, suggests that newly formed metasomatic minerals precipitated from the fenitizing fluids along the flow path. These orientations differ from the isotropic textures defined by primary (magmatic) minerals like pyrochlore, tetraferriphlogopite, dolomite, and calcite. However, and despite the microstructural differences between magmatic and carbohydrothermal phlogopite, their mineral chemistry is similar, suggesting that fenites are almost synchronous to the emplacement of carbonatites. These data indicate that fenites provide a rich archive of alkali-rich fluid infiltration around Nb-REE-rich carbonatite intrusions.
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    Origin of carbonatite-related niobium deposits: Insights from pyrochlore geochemistry
    (2024) Velasquez-Ruiz, Felipe; Reich, Martin; Broom-Fendley, Sam; Beard, Charles D.; Barra, Fernando; Romero, Rurik; Cordeiro, Pedro
    The carbonatite-related Nb deposits of the Alto Parana & iacute;ba Igneous Province (APIP) in central Brazil, currently account for similar to 92 % of the global Nb production. In the APIP, pyrochlore is abundant in magnet-ite-apatite-tetraferriphlogopite +/- carbonate rocks or phoscorites, occurring as interbedded layers with carbo-natites in the lower hypogene zone, feeding dike swarms of phoscorite and calcite carbonatite, and late-stage carbothermal veins in the upper hypogene zone. The origin of the phoscorite-carbonatite association can be explained by three hypotheses: (1) crystal segregation from fractional crystallization, (2) liquid immiscibility, and/or (3) phoscoritic magma formation after basement metasomatism (fenitization). However, it is not well understood whether pyrochlore formation is limited to a carbonatitic event, carbohydrothermal, or both, and this gap of knowledge is addressed in this work. To investigate the petrogenesis of pyrochlore-rich phoscorite, cathodoluminescence (CL) images, chemical maps, and LA-ICP-MS data were acquired of pyrochlore crystals from magmatic and carbothermal rocks from the Boa Vista Nb mine, Catalao II Complex. In the Boa Vista mine, oscillatory and patchy zoning were identified as primary pyrochlore textures commonly recorded at the lower hypogene zone, while secondary dissolution, skeletal and zonation-free textures are registered at shallower depths in the upper hypogene zone. Calciopyrochlore is the dominant Nb phase at the Boa Vista mine, with only two kenopyrochlore outliers. The pyrochlore CI chondrite-normalized REE distribution is consistent with geochemical results of the carbonatite and phoscorite rocks, indicating a magmatic origin for pyrochlore and the presence of pyrochlore antecrysts in carbothermal veins. The Sr/Y vs La and Na vs Ce diagrams in pyrochlore indicate a continuous fractionation pattern, with some mixtures of antecrysts and primary phases. An exami-nation of intercumulus calcite using CL provide evidence of carbonatitic magma residues within tetraferri-phlogopite phoscorite dikes and suggests that alkaline-carbonate-rich fluids played a role in transporting heavy minerals (i.e., magnetite, apatite, pyrochlore). Consequently, the textural and chemical evidence in the Boa Vista Nb mine indicates that the origin of pyrochlore-rich phoscorites is the result of physical segregation of heavy minerals from a carbonatite magma by fractional crystallization, leading to the emplacement of pyrochlore-rich carbonatite and phoscorite dikes. The implications at Catalao II may extend to other APIP alkaline-carbonatite complexes, as they share a genetic connection, and should motivate further studies focusing on pyrochlore geochemistry in other carbonatite-related Nb deposits, which will be crucial for advancing our knowledge of global Nb metallogenesis.
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    Regolith-hosted rare earth exploration in the Chilean Coastal Range of the Central Andes
    (2022) Bustos, Nicolas; Marquardt, Carlos; Belmar, Alex; Cordeiro, Pedro
    Regolith-hosted rare earth element deposits (RH-REE) are well-known in Asia, especially China, and are becoming increasingly important with the growing global demand for such metals. Ore formation controls of these deposits in Asia, which include sub-tropical to temperate climate, and mainly calc-alkaline granites with variable HREE and LREE bearing-minerals, are used to search for compatible exploration targets. However, the poor understanding of parameters controlling the formation of RH-REE mineralization outside China, e.g., Chile, might be hindering exploration efforts world-wide. This work addresses RH-REE mineralization in the Nahuelbuta Range, the local name of the Chilean Coastal Range between the Biobio and Araucania regions. The studied prospect is associated with late Carboniferous-early Permian I-type biotite tonalite and amphibole-biotite tonalite. Mineralogical analysis (TIMA-X) indicates that allanite and monazite are the main REE-bearing minerals in the host rocks. The regolith in the study area is up to 60 m deep and contains an exchangeable-REE concentration up to 2000 ppm, as determined by portable X-ray fluorescence (pXRF) and ICP-MS. The mineralization is divided into two types: 1) Preserved regoliths (e.g. drillhole RLS-09) where mineralization is HREEdominant (56% of total REE, (La/Yb)N -2) and is covered by a leached upper pedolith; and 2) partially eroded regoliths (e.g. drillhole RLS-07) where mineralization is LREE-dominant (58% of total REE, (La/Yb)N -4) and exposed. A morphometric analysis (SCM and swath profiles) and two 3D models (geomorphic and geochemical) indicate the current preservation of pediments and ore. Analyses of the exchangeable REE-fraction show that pedogenesis, leading to the deposit, is associated with REE-fractionation processes, most notably: a positive cerium anomaly (Ce/Ce*) in the upper pedolith and preferential adsorption of LREE at shallower depths, revealed by decreasing (La/Yb)N ratio with depth. We propose a mineralization model where the advance of the pedolith/saprolith horizon during progressive weathering and the breakdown of allanite and monazite was responsible for the neoformation of RH-REE clays at the base of the pedolith. Additionally, the landscape evolution of the Nahuelbuta Range controlled the preservation of ore bodies, which are either cropping out or hidden underneath the upper pedolith. A good understanding of the interplay between tonalite regolith development controls and regolith preservation during landscape evolution provide a strategy for REE exploration in the region. Moreover, the search for pediplains on suitable lithologies, mapping of regolith profiles, and their analysis via pXRF in the field by quantifying yttrium, appears to be a suitable strategy for early exploration of RH-REE deposits in the Chilean Coastal Range.
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    The 2.26 to 2.18 Ga Arc-Related Magmatism of the Almas-Conceicao do Tocantins Domain: An Early Stage of the Sao Francisco Paleocontinent Assembly in Central Brazil
    (2020) Saboia, Andre Menezes; de Oliveira, Claudinei Gouveia; Dantas, Elton Luis; Scandolara, Jaime Estevao; Cordeiro, Pedro; Rodrigues, Joseneusa Brilhante; Cordeiro de Sousa, Isabela Moreno
    Paleoproterozoic (Rhyacian) rocks dominate within the basement of the Neoproterozoic Brasilia Belt and their genesis has been attributed to the orogenic amalgamation event that assembled the Sao Francisco-Congo paleocontinent from 2.18 to 2.07 Ga. However, the tectonic framework and genesis of the building blocks involved in this continent-wide amalgamation event are unclear, particularly in relation to terranes from the Almas-Conceicao do Tocantins Domain, in the Goi ' as Massif, central Brazil. This work provides new whole-rock chemical and geochronological data, which indicate the generation of felsic to intermediate magmatism around 2.29 and 2.28 Ga corresponding to the Monzogranitic Unit and the Quartz-dioritic Suite, respectively. Later magmatic events occurred in a continental arc setting, around 2.26 to 2.2 Ga represented by metaluminous to peraluminous I-type magmatism of the Granodioritic to Tonalitic Suite (GTS) and the Serra do Boqueirao Suite. Around 2.2 to 2.18 Ga a peraluminous I-type magmatism took place and generated the Peraluminous Suite (PS). Our data show that after an earlier Siderian magmatic event around 2.45-2.34 Ga, reported in previous works, the Almas do Conceicao do Tocantins Domain oversaw additional Rhyacian events of magmatic activity around 2.29 Ga to 2.18 Ga. Regional geotectonic correlations with the Sao Francisco Craton and other pericratonic belts indicate coeval magmatic events taking place during the early stages of the Columbia Supercontinent amalgamation.
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    The carbonate-hosted Gortdrum Cu-Ag(?Sb-Hg) deposit, SW Ireland: C-O-Sr-Nd isotopes and whole-rock geochemical signatures
    (2023) Cordeiro, Pedro; dos Santos, Anderson Matias; Steed, Geoffrey; Silva, Andressa de Araujo; Meere, Patrick; Corcoran, Loretta; Simonetti, Antonio; Unitt, Richard
    The Gortdrum Cu-Ag(+/- Sb-Hg) deposit, consisted of a fault-controlled orebody (3.8 Mt @ 1.19 % Cu and 25.1 g/t Ag) formed at the base of the Irish Midlands basin, in Lower Carboniferous rocks laterally time equivalent to Navan Group rocks hosting the giant Navan Zn-Pb deposit, and form the base of the Irish Midlands basin. The ore body is hosted on the hanging-wall of the Gortdrum Fault either along strata or within a wedge of brecciated carbonate rocks. Vertical zonation based on predominant host rock, ore textures, sulfide assemblages, and whole -rock geochemistry allowed the detailing of three ore types: a) the lower ore, representing Cu sulfides hosted within basal carbonated siliciclastic rocks; b) the upper ore, representing Cu, Cu-Sb, and Hg sulfides hosted within upper calcareous rocks and; c) the vein-associated ore, dominantly hosted in the more competent upper carbonate rocks. The origin of the deposit is unambiguously related to the development of the Gortdrum Fault and its associated permeability, which allowed basement/basin-derived fluids to react with carbonates and induce copper-silver mineralization. The mineralogy, ore shoot geometry, and geochemical association of Gortdrum are shared with classic Zn-Pb Irish-type deposits such as Navan, Lisheen, Silvermines, and Tynagh (sub-seafloor replacement). In these Irish-type deposits, copper-silver mineralization is associated with the late stage of Zn-Pb mineralization and shares a common geochemical footprint with Gortdrum of anomalous Ag, As, Sb and Hg. Additionally, the C-O and Sr-Nd isotope range of Gortdrum and Navan samples overlap, indicating that mineralization processes in both deposits were ineffective in modifying the original host-rock signature. These similarities suggest that Gortdrum could represent a variation of Irish-type mineralization where late-stage Cu-Ag-Sb-bearing fluids succeeded in forming a deposit. Hypothetical early-stage Zn-Pb fluids a) never existed; b) deposited disseminated sulfides in country-rocks, c) formed an undiscovered resource or, d) deposited ore concentrations that were eroded off.
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    The Carbonate-Hosted Tullacondra Cu-Ag Deposit, Mallow, Ireland
    (2021) Silva, Andressa A.; Cordeiro, Pedro; Johnson, Sean C.; Lagoeiro, Leonardo E.; Corcoran, Loretta; Simonetti, Antonio; Meere, Patrick A.; Unitt, Richard; Colaco, Laisa Stingelin; Santos, Anderson M.
    The Tullacondra Cu-Ag deposit is located on the southern margin of the Lower Carboniferous Irish Midlands orefield and contains historical reserves of approximately 4.2 Mt at 0.7% Cu and 27.5 ppm Ag. The deposit is hosted within the hanging wall of a feeder fault, the EW-trending Tullacondra Fault, where sulfides and sulfosalts containing elevated Cu, Ag, As, and Sb deposited, whereas Zn and Pb are nearly absent. The deposition of Cu sulfides in Tullacondra took place along bedding and bedding-parallel dissolution seams, suggesting an epigenetic mineralization that formed: (a) the Transition Series-hosted mineralized zone containing elevated Cu associated with Ag, As, and Sb; (b) the Lower Limestone Shale-hosted mineralized zone, Cu-dominated and depleted in other metals, and (c) a near-vertical mineralized zone associated with fractures related to the Tullacondra Fault. Some similarities are shared with Irish-type Zn-Pb deposits, such as structural and stratigraphic controls, and elevated Cu, Ag, As, and Sb within feeder-fault proximal zones (such as in Lisheen and Silvermines). Whether Tullacondra mineralization was part of the Irish-type system or not, our deposit geometry evaluation, whole-rock geochemistry, paragenetic sequence, and texture relationships indicate that Cu-Ag deposition involved the reaction of metal-bearing fluids with carbonate rocks.
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    The Carbonatite-Related Morro do Padre Niobium Deposit, Cataldo II Complex, Central Brazil
    (2022) Palmieri, Matheus; Brod, Jose Affonso; Cordeiro, Pedro; Gaspar, Jose Carlos; Ribeiro Barbosa, Paulo Afonso; de Assis, Luis Carlos; Junqueira-Brod, Tereza Cristina; Eduardo e Silva, Serio; Milanezi, Bruno Palhares; Machado, Sergio Augusto; Jacomo, Marta Henriques
    The Morro do Padre deposit contains a valuable niobium resource estimated at 14.5 Mt at 1.52 wt % Nb2O5 (at a cut-off grade of 0.5% Nb2O5) hosted in carbonatite-related rocks and their regolith in the southern part of the Catalao II Complex, in central Brazil. Morro do Padre shares numerous geologic features with some of the biggest niobium producers in the world (the Boa Vista mine, also in Catalao II, the Mina II in Catalao I, and the CBMM mine in the Araxa Complex) and can help advance our understanding of the ore formation processes involved. The Morro do Padre hypogene zone is characterized by E-W-trending dike swarms of tetraferri-phlogopite phoscorites (magnetite-apatite-carbonate-tetraferriphlogopite-pyrochlore rocks) and carbonatites intrusive within Precambrian rocks. The magmatic origin of these Nb-rich rocks is supported by country rock xenoliths within dikes and ponding into a stratified sill with repetitive cumulus layers. At least two tetraferri-phlogopite phoscorite phases (apatite-rich or pegmatoidal P1 and the magnetite-rich P2) and two carbonatite phases (C1 calcite carbonatite and C2 dolomite carbonatite) are present. The bulk of hypogene mineralization is primarily controlled by the emplacement of P2 dikes and secondarily by C1 and C2 dikes where pyrochlore is accessory. Whole-rock and pyrochlore chemistry and textural and spatial relationships suggest that the genesis of P2 (and that of the niobium deposit) is due to the emplacement of a parental dolomite carbonatite magma that crystallized medium-to coarse-grained magnetite, apatite, tetraferriphlogopite, and pyrochlore on dike walls upon cooling, in an elaborate magmatic type of "cumulate dike build-up. " Weathering generated the regolith zone, where the dissolution of barren phases compounded the Nb concentration even further. Morro do Padre showcases the role of carbonatite-phoscorite magmatism in producing Fe-P-Nb-rich rocks and economic niobium mineralization.
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    The genetic link between kamafugite magmatism and alkaline-carbonatite complexes in the Late Cretaceous Alto Paranaiba Igneous Province, Central Brazil
    (2023) Velasquez Ruiz, Felipe; Cordeiro, Pedro; Reich, Martin; Motta, Joao Gabriel; Ribeiro, Carlos Cordeiro; Angerer, Thomas; Bernardes, Renato Borges
    The Late Cretaceous Mata da Corda Formation, located in the eastern part of the Alto Paranaiba Igneous Province (APIP), Central Brazil, is one of the few places on Earth where kamafugite melts reached the surface generating large volumes of lava, pyroclastic rocks and shallow intrusions over an area of 4,500 km(2). The western part of the APIP, however, is dominated by hundreds of diatreme-like kamafugites and shallow kimberlite intrusions and by the occurrence of multi-stage alkaline-carbonatite complexes. These complexes feature silica-undersaturated K-rich alkaline rocks, such as aillikite, that closely resemble the mineralogy and geochemistry of kamafugite, albeit lacking feldspathoids. The spatial and temporal distribution of kamafugite and aillikite within the APIP suggests a connection between them. In addition, on a regional scale, airborne magnetic data show three highly magnetic dipole-like structures to the south of the Mata da Corda Formation of an undisclosed nature, which bear geophysical similar responses to the neighbouring alkaline-carbonatite complexes. Links between kamafugite and aillikite are evaluated by the following chemical and isotopic evidence: (1) kamafugite and aillikite compositions plot in the kamafugite field of Foley's ultrapotassic rock classification; (2) similar CI chondrite-normalized REE distribution, with aillikite enriched up to 2 times in REE compared to kamafugite; (3) both lithologies share almost the same rock-forming minerals; and (4) similar Nd-143/Nd-144((i)) and Sr-87/Sr-86((i)) ratios for all the APIP alkaline-carbonatite rocks, indicating a common source from an enriched lithospheric mantle. Therefore, silica-undersaturated rocks from alkaline-carbonatite complexes display an evolved ultrapotassic affinity indicative of a genetic link.
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    The Siderian crust (2.47-2.3 Ga) of the Goias Massif and its role as a building block of the Sao Francisco paleocontinent
    (2020) Saboia, Andre Menezes; de Oliveira, Claudinei Gouveia; Dantas, Elton Luiz; Cordeiro, Pedro; Scandolara, Jaime Estevao; Rodrigues, Joseneusa Brilhante; Cordeiro de Sousa, Isabela Moreno
    The basement of the northern Brasilia Belt, in Central Brazil, is dominated by large volumes of TTG magmatism generated during the Early Paleoproterozoic, and represents a continental block formed prior to the welding of the Sao Francisco paleocontinent during the Rhyacian, holding important information concerning the mechanisms and products of Paleoproterozoic crustal growth and amalgamation. New U-Pb zircon geochronological data was obtained from metagranitoids and mafic-ultramafic intrusions from the Almas-Conceicao do Tocantins Domain (ACTD). This was coupled with geochemical data from the metagranitoids to better constrain the processes of continental crust evolution in this region during the Siderian period. Two main plutonic episodes were recognized in the mapped area: (i) an early suite (2.47 Ga) dominated by tonalites and trondhjemites with subordinate biotite granites (Ribeirao das Areias Complex - RAC); and (ii) a later suite (2.30 Ga) including tonalites and trondhjemites (Ribeirao Itaboca Suite - RIS). Most of the RAC trondhjemite-tonalite-granodiorite (TTG) rocks are marked by fractionated REE patterns with high (La/Yb)(N) = 15-107 and samples have medium to high Sr/Y ratio (28-257). These TTG include both high- and low-Al types and high- and medium-pressure groups. The RIS TTG suite displays higher HREE contents with high (La/Yb)(N) = 65-89 and high Sr/Y ratio (59-95) and contains the high-Al type and the medium pressure group. In spite of the wide age gap between them, both RAC and RIS are characterized by TTG rocks formed in a subduction-like tectonic setting. The biotite granites are related to a magmatic stage after the TTG formation. Mafic rocks of the Gameleira Suite have an abundance of zircon, interpreted as crustal contamination, with dominant (207)pb/(206)pb age populations of 2.48 and 2.30 Ga, and are interpreted to be associated with an extensional magmatic event following the Siderian period. Regional geotectonic correlations within the Sao Francisco Craton based on data compiled from the literature indicate a significant volume of Siderian crust generation that has been overlooked in continental amalgamation models and that TTG magmatism is a more common geochemical signature in Paleoproterozoic rocks than has been previously suggested.
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    The western Sao Francisco pericraton interpreted from crustal magnetic and gravity sources
    (2020) Oliveira dos Reis, Luciane Katiuscia; Vidotti, Roberta Mary; Cordeiro, Pedro; de Oliveira, Claudinei Gouveia
    The Neoproterozoic Brasiliano Orogeny shaped the former Sao Francisco paleocontinent into a preserved cratonic nucleus surrounded by a pericratonic region. In central Brazil, this pericraton crops out as the Goias Massif, the basement of the northern Brasilia Belt. The well-known difficulty of tracing suture zones on surface led to a longstanding dispute on whether the Rio Maranhao Thrust, a structure separating the Internal Zone and the External Zone of the Brasilia Belt, marked the Brasiliano suture. This interpretation was largely based on regional gravimetric data showing a steep discontinuity at depth, between these zones. However, the Rio Maranhao Thrust separates two pericratonic domains of the Goias Massif (Campinorte Domain and Cavalcante-Arraias Domain), which otherwise share similar Paleoproterozoic ages and geology. To properly address the main structural boundaries within the northern Brasilia Belt, this work was focused on comparing shallow and deep gravity and magnetic data processed as enhanced anomalies and through matched filter analysis. Our results show that the large mafic-ultramafic complexes within the Internal Zone of the Brasilia Belt are masking a smooth gravimetric transition into the External Zone. Additionally, the alleged suture zone is coincident with the Mesoproterozoic rift-related Juscelandia and Palmeiropolis volcano-sedimentary sequences, which have been largely ignored in their role as creating magnetic and gravity suture-like signatures. Along with previous structural and geochronological data, our results argue against the Rio Maranhao Thrust as a suture zone and, instead, support the alternative interpretation of the thrust as an intracontinental feature within a portion of the Sao Francisco pericraton. This pericratonic region, unliked the preserved cratonic core, was widely affected by Mesoproterozoic rifting and Neoproterozoic thick-skinned thrusting. The Rio Parana Thrust, on the other hand, is unnoticeable below 8 km depth in gravity and magnetic data, suggesting thin-skinned tectonics also associated with the Brasiliano Orogeny. Finally, the relative crustal homogeneity from the Sao Francisco craton into the Goias Massif evidenced by our gravity data and confirmed by first- and second-order magnetic lineaments confirms the nature of a pericraton with dominantly NE (N20-40E) trending lineaments. These lineaments were progressively overprinted by Brasiliano NNE (N45-70E) structures from the western margin of the External Zone into the Internal Zone.